The proteases may be categorized into families by the different amino acid sequences (generally between 2 and 10 residues) located on either side of the cleavage site of the protease.
The proper functioning of the cell requires careful control of the levels of important structural proteins, enzymes, and regulatory proteins. One of the ways that cells can reduce the steady state level of a particular protein is by proteolytic degradation. Further, one of the ways cells produce functioning proteins is to produce pre or pro-protein precursors that are processed by proteolytic degradation to produce an active moiety. Thus, complex and highly-regulated mechanisms have been evolved to accomplish this degradation.
Proteases regulate many different cell proliferation, differentiation, and signaling processes by regulating protein turnover and processing. Uncontrolled protease activity (either increased or decreased) has been implicated in a variety of disease conditions including inflammation, cancer, arteriosclerosis, and degenerative disorders.
An additional role of intracellular proteolysis is in the stress-response. Cells that are subject to stress such as starvation, heat-shock, chemical insult or mutation respond by increasing the rates of proteolysis. One function of this enhanced proteolysis is to salvage amino acids from non-essential proteins. These amino acids can then be re-utilized in the synthesis of essential proteins or metabolized directly to provide energy. Another function is in the repair of damage caused by the stress. For example, oxidative stress has been shown to damage a variety of proteins and cause them to be rapidly degraded.
The International Union of Biochemistry and Molecular Biology (IUBMB) has recommended to use the term peptidase for the subset of peptide bond hydrolases (Subclass E.C 3.4.). The widely used term protease is synonymous with peptidase. Peptidases comprise two groups of enzymes: the endopeptidases and the exopeptidases, which cleave peptide bonds at points within the protein and remove amino acids sequentially from either N or C-terminus respectively. The term proteinase is also used as a synonym word for endopeptidase and four mechanistic classes of proteinases are recognized by the IUBMB: two of these are described below (also see: Handbook of Proteolytic Enzymes by Barrett, Rawlings, and Woessner A P Press, NY 1998). Also, for a review of the various uses of proteases as drug targets, see: Weber M, Emerging treatments for hypertension: potential role for vasopeptidase inhibition; Am J Hypertens 1999 November;12(11 Pt 2):139S–147S; Kentsch M, Otter W, Novel neurohormonal modulators in cardiovascular disorders. The therapeutic potential of endopeptidase inhibitors, Drugs R D 1999 April;1(4):331–8; Scarborough R M, Coagulation factor Xa: the prothrombinase complex as an emerging therapeutic target for small molecule inhibitors, J Enzym Inhib 1998;14(1):15–25; Skotnicki J S, et al., Design and synthetic considerations of matrix metalloproteinase inhibitors, Ann N Y Acad Sci 1999 Jun. 30;878:61–72; McKerrow J H, Engel J C, Caffrey C R, Cysteine protease inhibitors as chemotherapy for parasitic infections, Bioorg Med Chem 1999 April;7(4):639–44; Rice K D, Tanaka R D, Katz B A, Numerof R P, Moore W R, Inhibitors of tryptase for the treatment of mast cell-mediated diseases, Curr Pharm Des 1998 October;4(5):381–96; Materson B J, Will angiotensin converting enzyme genotype, receptor mutation identification, and other miracles of molecular biology permit reduction of NNT Am J Hypertens 1998 August;11(8 Pt 2):138S–142S
Serine Proteases
The serine proteases (SP) are a large family of proteolytic enzymes that include the digestive enzymes, trypsin and chymotrypsin, components of the complement cascade and of the blood-clotting cascade, and enzymes that control the degradation and turnover of macromolecules of the extracellular matrix. SP are so named because of the presence of a serine residue in the active catalytic site for protein cleavage. SP have a wide range of substrate specificities and can be subdivided into subfamilies on the basis of these specificities. The main sub-families are trypases (cleavage after arginine or lysine), aspases (cleavage after aspartate), chymases (cleavage after phenylalanine or leucine), metases (cleavage after methionine), and serases (cleavage after serine).
A series of six SP have been identified in murine cytotoxic T-lymphocytes (CTL) and natural killer (NK) cells. These SP are involved with CTL and NK cells in the destruction of virally transformed cells and tumor cells and in organ and tissue transplant rejection (Zunino, S. J. et al. (1990) J. Immunol. 144:2001–9; Sayers, T. J. et al. (1994) J. Immunol. 152:2289–97). Human homologs of most of these enzymes have been identified (Trapani, J. A. et al. (1988) Proc. Natl. Acad. Sci. 85:6924–28; Caputo, A. et al. (1990) J. Immunol. 145:737–44). Like all SP, the CTL-SP share three distinguishing features:1) the presence of a catalytic triad of histidine, serine, and aspartate residues which comprise the active site; 2) the sequence GDSGGP which contains the active site serine; and 3) an N-terminal IIGG sequence which characterizes the mature SP.
The SP are secretory proteins which contain N-terminal signal peptides that serve to export the immature protein across the endoplasmic reticulum and are then cleaved (von Heijne (1986) Nuc. Acid. Res. 14:5683–90). Differences in these signal sequences provide one means of distinguishing individual SP. Some SP, particularly the digestive enzymes, exist as inactive precursors or preproenzymes, and contain a leader or activation peptide sequence 3′ of the signal peptide. This activation peptide may be 2–12 amino acids in length, and it extends from the cleavage site of the signal peptide to the N-terminal IIGG sequence of the active, mature protein. Cleavage of this sequence activates the enzyme. This sequence varies in different SP according to the biochemical pathway and/or its substrate (Zunino et al, supra; Sayers et al, supra). Other features that distinguish various SP are the presence or absence of N-linked glycosylation sites that provide membrane anchors, the number and distribution of cysteine residues that determine the secondary structure of the SP, and the sequence of a substrate binding sites such as S′. The S′ substrate binding region is defined by residues extending from approximately +17 to +29 relative to the N-terminal I (+1). Differences in this region of the molecule are believed to determine SP substrate specificities (Zunino et al, supra).
Trypsinogens
The trypsinogens are serine proteases secreted by exocrine cells of the pancreas (Travis J and Roberts R. Biochemistry 1969; 8: 2884–9; Mallory P and Travis J, Biochemistry 1973; 12: 2847–51). Two major types of trypsinogen isoenzymes have been characterized, trypsinogen-1, also called cationic trypsinogen, and trypsinogen-2 or anionic trypsinogen. The trypsinogen proenzymes are activated to trypsins in the intestine by enterokinase, which removes an activation peptide from the N-terminus of the trypsinogens. The trypsinogens show a high degree of sequence homology, but they can be separated on the basis of charge differences by using electrophoresis or ion exchange chromatography. The major form of trypsinogen in the pancreas and pancreatic juice is trypsinogen-1 (Guy C O et al., Biochem Biophys Res Commun 1984; 125: 516–23). In serum of healthy subjects, trypsinogen-1 is also the major form, whereas in patients with pancreatitis, trypsinogen-2 is more strongly elevated (Itkonen et al., J Lab Clin Med 1990; 115:712–8). Trypsinogens also occur in certain ovarian tumors, in which trypsinogen-2 is the major form (Koivunen et al., Cancer Res 1990; 50: 2375–8). Trypsin-1 in complex with alpha-1-antitrypsin, also called alpha-1-antiprotease, has been found to occur in serum of patients with pancreatitis (Borgstrom A and Ohlsson K, Scand J Clin Lab Invest 1984; 44: 381–6) but determination of this complex has not been found useful for differentiation between pancreatic and other gastrointestinal diseases (Borgstrom et al., Scand J Clin Lab Invest 1989; 49:757–62).
Trypsinogen-1 and -2 are closely related immunologically (Kimland et al., Clin Chim Acta 1989; 184: 31–46; Itkonen et al., 1990), but by using monoclonal antibodies (Itkonen et al., 1990) or by absorbing polyclonal antisera (Kimland et al., 1989) it is possible to obtain reagents enabling specific measurement of each form of trypsinogen.
When active trypsin reaches the blood stream, it is inactivated by the major trypsin inhibitors alpha-2-macroglobulin and alpha-1-antitrypsin (AAT). AAT is a 58 kilodalton serine protease inhibitor synthesized in the liver and is one of the main protease inhibitors in blood. Whereas complexes between trypsin-1 and AAT are detectable in serum (Borgstrom and Ohlsson, 1984) the complexes with alpha-2-macroglobulin are not measurable with antibody-based assays (Ohlsson K, Acta Gastroenterol Belg 1988; 51: 3–12).
Inflammation of the pancreas or pancreatitis may be classified as either acute or chronic by clinical criteria. With treatment, acute pancreatitis can often be cured and normal function restored. Chronic pancreatitis often results in permanent damage. The precise mechanisms which trigger acute inflammation are not understood. However, some causes in the order of their importance are alcohol ingestion, biliary tract disease, post-operative trauma, and hereditary pancreatitis. One theory provides that autodigestion, the premature activation of proteolytic enzymes in the pancreas rather than in the duodenum, causes acute pancreatitis. Any number of other factors including endotoxins, exotoxins, viral infections, ischemia, anoxia, and direct trauma may activate the proenzymes. In addition, any internal or external blockage of pancreatic ducts can also cause an accumulation of pancreatic juices in the pancreas resulting cellular damage.
Anatomy, physiology, and diseases of the pancreas are reviewed, inter alia, in Guyton A C (1991) Textbook of Medical Physiology, W B Saunders Co, Philadelphia Pa.; Isselbacher K J et al (1994) Harrison's Principles of Internal Medicine, McGraw-Hill, New York City; Johnson K E (1991) Histology and Cell Biology, Harwal Publishing, Media Pa.; and The Merck Manual of Diagnosis and Therapy (1992) Merck Research Laboratories, Rahway N.J.
Metalloprotease
The metalloproteases may be one of the older classes of proteinases and are found in bacteria, fungi as well as in higher organisms. They differ widely in their sequences and their structures but the great majority of enzymes contain a zinc atom which is catalytically active. In some cases, zinc may be replaced by another metal such as cobalt or nickel without loss of the activity. Bacterial thermolysin has been well characterized and its crystallographic structure indicates that zinc is bound by two histidines and one glutamic acid. Many enzymes contain the sequence HEXXH, which provides two histidine ligands for the zinc whereas the third ligand is either a glutamic acid (thermolysin, neprilysin, alanyl aminopeptidase) or a histidine (astacin). Other families exhibit a distinct mode of binding of the Zn atom. The catalytic mechanism leads to the formation of a non covalent tetrahedral intermediate after the attack of a zinc-bound water molecule on the carbonyl group of the scissile bond. This intermediate is further decomposed by transfer of the glutamic acid proton to the leaving group.
Metalloproteases contain a catalytic zinc metal center which participates in the hydrolysis of the peptide backbone (reviewed in Power and Harper, in Protease Inhibitors, A. J. Barrett and G. Salversen (eds.) Elsevier, Amsterdam, 1986, p. 219). The active zinc center differentiates some of these proteases from calpains and trypsins whose activities are dependent upon the presence of calcium. Examples of metalloproteases include carboxypeptidase A, carboxypeptidase B, and thermolysin.
Metalloproteases have been isolated from a number of procaryotic and eucaryotic sources, e.g. Bacillus subtilis (McConn et al., 1964, J. Biol. Chem. 239:3706); Bacillus megaterium; Serratia (Miyata et al., 1971, Agr. Biol. Chem. 35:460); Clostridium bifermentans (MacFarlane et al., 1992, App. Environ. Microbiol. 58:1195–1200), Legionella pneumophila (Moffat et al., 1994, Infection and Immunity 62:751–3). In particular, acidic metalloproteases have been isolated from broad-banded copperhead venoms (Johnson and Ownby, 1993, Int. J. Biochem. 25:267–278), rattlesnake venoms (Chlou et al., 1992, Biochem. Biophys. Res. Commun. 187:389–396) and articular cartilage (Treadwell et al., 1986, Arch. Biochem. Biophys. 251:715–723). Neutral metalloproteases, specifically those having optimal activity at neutral pH have, for example, been isolated from Aspergillus sojae (Sekine, 1973, Agric. Biol. Chem. 37:1945–1952). Neutral metalloproteases obtained from Aspergillus have been classified into two groups, npI and npII (Sekine, 1972, Agric. Biol. Chem. 36:207–216). So far, success in obtaining amino acid sequence information from these fungal neutral metalloproteases has been limited. An npII metalloprotease isolated from Aspergillus oryzae has been cloned based on amino acid sequence presented in the literature (Tatsumi et al., 1991, Mol. Gen. Genet. 228:97–103). However, to date, no npI fungal metalloprotease has been cloned or sequenced. Alkaline metalloproteases, for example, have been isolated from Pseudomonas aeruginosa (Baumann et al., 1993, EMBO J 12:3357–3364) and the insect pathogen Xenorhabdus luminescens (Schmidt et al., 1998, Appl. Environ. Microbiol. 54:2793–2797).
Metalloproteases have been devided into several distinct families based primarily on activity and sturcture:1) water nucleophile; water bound by single zinc ion ligated to two His (within the motif HEXXH) and Glu, His or Asp; 2) water nucleophile; water bound by single zinc ion ligated to His, Glu (within the motif HXXE) and His; 3) water nucleophile; water bound by single zinc ion ligated to His, Asp and His; 4) Water nucleophile; water bound by single zinc ion ligated to two His (within the motif HXXEH) and Glu and 5) water nucleophile; water bound by two zinc ions ligated by Lys, Asp, Asp, Asp, Glu.
Examples of members of the metalloproteinase family include, but are not limited to, membrane alanyl aminopeptidase (Homo sapiens), germinal peptidyl-dipeptidase A (Homo sapiens), thimet oligopeptidase (Rattus norvegicus), oligopeptidase F (Lactococcus lactis), mycolysin (Streptomyces cacaoi), immune inhibitor A (Bacillus thuringiensis), snapalysin (Streptomyces lividans), leishmanolysin (Leishmania major), microbial collagenase (Vibrio alginolyticus), microbial collagenase, class I (Clostridium perfringens), collagenase 1 (Homo sapiens), serralysin (Serratia marcescens), fragilysin (Bacteroides fragilis), gametolysin (Chlamydomonas reinhardtii), astacin (Astacus fluviatilis), adamalysin (Crotalus adamanteus), ADAM 10 (Bos taurus), neprilysin (Homo sapiens), carboxypeptidase A (Homo sapiens), carboxypeptidase E (Bos taurus), gamma-D-glutamyl-(L)-meso-diaminopimelate peptidase I (Bacillus sphaericus), vanY D-Ala-D-Ala carboxypeptidase (Enterococcus faecium), endolysin (bacteriophage A118), pitrilysin (Escherichia coli), mitochondrial processing peptidase (Saccharomyces cerevisiae), leucyl aminopeptidase (Bos taurus), aminopeptidase I (Saccharomyces cerevisiae), membrane dipeptidase (Homo sapiens), glutamate carboxypeptidase (Pseudomonas sp.), Gly-X carboxypeptidase (Saccharomyces cerevisiae), O-sialoglycoprotein endopeptidase (Pasteurella haemolytica), beta-lytic metalloendopeptidase (Achromobacter lyticus), methionyl aminopeptidase I (Escherichia coli), X-Pro aminopeptidase (Escherichia coli), X-His dipeptidase (Escherichia coli), IgA1-specific metalloendopeptidase (Streptococcus sanguis), tentoxilysin (Clostridium tetani), leucyl aminopeptidase (Vibrio proteolyticus), aminopeptidase (Streptomyces griseus), IAP aminopeptidase (Escherichia coli), aminopeptidase T (Thermus aquaticus), hyicolysin (Staphylococcus hyicus), carboxypeptidase Taq (Thermus aquaticus), anthrax lethal factor (Bacillus anthracis), penicillolysin (Penicillium citrinum), fungalysin (Aspergillus fumigatus), lysostaphin (Staphylococcus simulans), beta-aspartyl dipeptidase (Escherichia coli), carboxypeptidase Ss1 (Sulfolobus solfataricus), FtsH endopeptidase (Escherichia coli), glutamyl aminopeptidase (Lactococcus lactis), cytophagalysin (Cytophaga sp.), metalloendopeptidase (vaccinia virus), VanX D-Ala-D-Ala dipeptidase (Enterococcus faecium), Ste24p endopeptidase (Saccharomyces cerevisiae), dipeptidyl-peptidase III (Rattus norvegicus), S2P protease (Homo sapiens), sporulation factor SpoIVFB (Bacillus subtilis), and HYBD endopeptidase (Escherichia coli).
Metalloproteases have been found to have a number of uses. For example, there is strong evidence that a metalloprotease is involved in the in vivo proteolytic processing of the vasoconstrictor, endothelin-1. Rat metalloprotease has been found to be involved in peptide hormone processing. One important subfamily of the metalloproteases are the matrix metalloproteases.
A number of diseases are thought to be mediated by excess or undesired metalloprotease activity or by an imbalance in the ratio of the various members of the protease family of proteins. These include: a) osteoarthritis (Woessner, et al., J. Biol. Chem. 259(6), 3633, 1984; Phadke, et al., J. Rheumatol. 10, 852, 1983), b) rheumatoid arthritis (Mullins, et al., Biochim. Biophys. Acta 695, 117, 1983; Woolley, et al., Arthritis Rheum. 20, 1231, 1977; Gravallese, et al., Arthritis Rheum. 34, 1076, 1991), c) septic arthritis (Williams, et al., Arthritis Rheum. 33, 533, 1990), d) tumor metastasis (Reich, et al., Cancer Res. 48, 3307, 1988, and Matrisian, et al., Proc. Nat'l. Acad. Sci., USA 83, 9413, 1986), e) periodontal diseases (Overall, et al., J. Periodontal Res. 22, 81, 1987), f) corneal ulceration (Bums, et al., Invest. Opthalmol. Vis. Sci. 30, 1569, 1989), g) proteinuria (Baricos, et al., Biochem. J. 254, 609, 1988), h) coronary thrombosis from atherosclerotic plaque rupture (Henney, et al., Proc. Nat'l. Acad. Sci., USA 88, 8154–8158, 1991), i) aneurysmal aortic disease (Vine, et al., Clin. Sci. 81, 233, 1991), j) birth control (Woessner, et al., Steroids 54, 491, 1989), k) dystrophobic epidermolysis bullosa (Kronberger, et al., J. Invest. Dermatol. 79, 208, 1982), and 1) degenerative cartilage loss following traumatic joint injury, m) conditions leading to inflammatory responses, osteopenias mediated by MMP activity, n) tempero mandibular joint disease, o) demyelating diseases of the nervous system (Chantry, et al., J. Neurochem. 50, 688, 1988).
Aspartic Protease
Aspartic proteases have been divided into several distinct families based primarily on activity and structure. These include 1) water nucleophile; water bound by two Asp from monomer or dimer; all endopeptidases, from eukaryote organisms, viruses or virus-like organisms and 2) endopeptidases that are water nucleophile and are water bound by Asp and Asn.
Most of aspartic proteases belong to the pepsin family. The pepsin family includes digestive enzymes such as pepsin and chymosin as well as lysosomal cathepsins D and processing enzymes such as renin, and certain fungal proteases (penicillopepsin, rhizopuspepsin, endothiapepsin). A second family comprises viral proteases such as the protease from the AIDS virus (HIV) also called retropepsin. Crystallographic studies have shown that these enzymes are bilobed molecules with the active site located between two homologous lobes. Each lobe contributes one aspartate residue of the catalytically active diad of aspartates. These two aspartyl residues are in close geometric proximity in the active molecule and one aspartate is ionized whereas the second one is unionized at the optimum pH range of 2–3. Retropepsins, are monomeric, i.e carry only one catalytic aspartate and then dimerization is required to form an active enzyme.
In contrast to serine and cysteine proteases, catalysis by aspartic protease do not involve a covalent intermediate though a tetrahedral intermediate exists. The nucleophilic attack is achieved by two simultaneous proton transfer: one from a water molecule to the diad of the two carboxyl groups and a second one from the diad to the carbonyl oxygen of the substrate with the concurrent CO—NH bond cleavage. This general acid-base catalysis, which may be called a “push-pull” mechanism leads to the formation of a non covalent neutral tetrahedral intermediate.
Examples of the aspartic protease family of proteins include, but are not limited to, pepsin A (Homo sapiens), HIV1 retropepsin (human immunodeficiency virus type 1), endopeptidase (cauliflower mosaic virus), bacilliform virus putative protease (rice tungro bacilliform virus), aspergillopepsin II (Aspergillus niger), thermopsin (Sulfolobus acidocaldarius), nodavirus endopeptidase (flock house virus), pseudomonapepsin (Pseudomonas sp. 101), signal peptidase II (Escherichia coli), polyprotein peptidase (human spumaretrovirus), copia transposon (Drosophila melanogaster), SIRE-1 peptidase (Glycine max), retrotransposon bs1 endopeptidase (Zea mays), retrotransposon peptidase (Drosophila buzzatii), Tas retrotransposon peptidase (Ascaris lumbricoides), Pao retrotransposon peptidase (Bombyx mori), putative proteinase of Skippy retrotransposon (Fusarium oxysporum), tetravirus endopeptidase (Nudaurelia capensis omega virus), presenilin 1 (Homo sapiens).
Proteases and Cancer
Proteases are critical elements at several stages in the progression of metastatic cancer. In this process, the proteolytic degradation of structural protein in the basal membrane allows for expansion of a tumor in the primary site, evasion from this site as well as homing and invasion in distant, secondary sites. Also, tumor induced angiogenesis is required for tumor growth and is dependent on proteolytic tissue remodeling. Transfection experiments with various types of proteases have shown that the matrix metalloproteases play a dominant role in these processes in particular gelatinases A and B (MMP-2 and MMP-9, respectively). For an overview of this field see Mullins, et al., Biochim. Biophys. Acta 695, 177, 1983; Ray, et al., Eur. Respir. J. 7, 2062, 1994; Birkedal-Hansen, et al., Crit. Rev. Oral Biol. Med. 4, 197, 1993.
Furthermore, it was demonstrated that inhibition of degradation of extracellular matrix by the native matrix metalloprotease inhibitor TIMP-2 (a protein) arrests cancer growth (DeClerck, et al., Cancer Res. 52, 701, 1992) and that TIMP-2 inhibits tumor-induced angiogenesis in experimental systems (Moses, et al. Science 248, 1408, 1990). For a review, see DeClerck, et al., Ann. N.Y. Acad. Sci. 732, 222, 1994. It was further demonstrated that the synthetic matrix metalloprotease inhibitor batimastat when given intraperitoneally inhibits human colon tumor growth and spread in an orthotopic model in nude mice (Wang, et al. Cancer Res. 54, 4726, 1994) and prolongs the survival of mice bearing human ovarian carcinoma xenografts (Davies, et. al., Cancer Res. 53, 2087, 1993). The use of this and related compounds has been described in Brown, et al., WO-9321942 A2.
There are several patents and patent applications claiming the use of metalloproteinase inhibitors for the retardation of metastatic cancer, promoting tumor regression, inhibiting cancer cell proliferation, slowing or preventing cartilage loss associated with osteoarthritis or for treatment of other diseases as noted above (e.g. Levy, et al., WO-9519965 A1; Beckett, et al., WO-9519956 A1; Beckett, et al., WO-9519957 A1; Beckett, et al., WO-9519961 A1; Brown, et al., WO-9321942 A2; Crimmin, et al., WO-9421625 A1; Dickens, et al., U.S. Pat. No. 4,599,361; Hughes, et al., U.S. Pat. No. 5,190,937; Broadhurst, et al., EP 574758 A1; Broadhurst, et al., EP 276436; and Myers, et al., EP 520573 A1.
Hepsin
Extracellular proteases mediate the digestion of neighboring extracellular matrix components in initial tumor growth, allow shedding or desquamation of tumor cells into the surrounding environment, provide the basis for invasion of basement membranes in target metastatic organs, and are required for release and activation of many growth and angiogenic factors. Experimental evidence indicates that hepsin, a cell surface serine protease identified in hepatoma cells, is overexpressed in ovarian cancer. Hepsin is a serine protease found in most tissues, abundant in the liver. It is a membrane associated protein and is not found in the cytosol. Hepsin does not appear to be essential for development or homeostasis. On Northern blot analysis, the hepsin transcript was abundant in carcinoma but was almost never expressed in normal adult tissue, including normal ovary, suggesting that hepsin is frequently overexpressed in ovarian tumors and therefore may be a candidate protease in the invasive process and growth capacity of ovarian tumor cells.
For more information, see: Tanimoto, et al., Cancer Res. 1997 July 15;57(14):2884–7; Leytus, et al., Biochemistry 27: 1067–1074, 1988, PubMed ID : 2835076; Tsuji, et al., J. Biol. Chem. 266: 16948–16953, 1991, PubMed ID :1885621; and Wu, Q., et al., J. Clin. Invest. 101: 321–326, 1998, PubMed ID :9435303.
Protease proteins, particularly members of the hepsin subfamily, are a major target for drug action and development. Accordingly, it is valuable to the field of pharmaceutical development to identify and characterize previously unknown members of this subfamily of protease proteins. The present invention advances the state of the art by providing a previously unidentified human protease proteins that have homology to members of the hepsin subfamily.